The field of the invention relates generally to optical fiber soldering, and more specifically, to methods and apparatus for making micro-soldered connections between optical fibers and optical components.
In certain laser diode applications, failures are often due to the broken optical fibers attached to the laser diode package, for example, a mini-dil (dual-in-line) laser diode package. During end use, solder voids and weak fiber sections can cause the optical fiber to break.
Currently, metalized fiber is soldered all the way to the end of a feed through tube (sometimes referred to as a snout) of the mini-dil laser diode package. Generally this soldering is done with an alloy of indium and tin (In 52% and Sn 48%). This alloy is sometimes referred to as In52Sn48 solder. In the soldering process, a fiber jacket for the optical fiber is placed at a distance of about five millimeters from the feed through tube, and a fiber boot is attached to both the fiber jacket and the feed through tube by epoxy. In this configuration, the fiber boot is the only strain relief for the exposed five millimeter region of the unjacketed optical fiber.
This configuration has certain problems associated therewith. For example, using In52Sn48 solder may result in voids inside the feed through tube, because In52Sn48 solder is a low melting point (about 118 degrees Celsius) soft solder which is prone to formation of voids. To prepare the end product, the In52 Sn48 solder is applied to the end of a window inside of the feed through tube, which is subsequently filled with unsoldered In52Sn48 to the end of the feed through tube. The fiber jacket, which is the main protection of the fragile glass fiber, is located five millimeters outside the feed through tube. The glass fiber is unprotected across this five millimeter distance.
As the fiber assembly gets handled during construction of the end device, the optical fiber within this five millimeter section is prone to breakage. More specifically, during a production process, these assemblies associated with the laser diodes and optical fibers are moved around when assembled into the end package. In addition, a foam excavation process also causes movement of the “unprotected” fiber within the assembly. As a result of the broken optical fibers within laser diode packages, certain end product yields are less than 50%.
By filling the entire feed through tube with solder, extra stress is exerted on the fiber because there is a large mismatch in the coefficient of thermal expansion (CTE) between the glass fiber and the metal solder. Since the primary function of the solder is to form a hermetic seal for the mini-dil package, it is not required to have the solder fill the entire feed through tube. An alternative design should consider using less solder to form the hermetic seal between the glass optical fiber and the laser diode package.
In addition, the fiber boot used in the current process may loosen over time. One cause is epoxy degradation and failure during an installation process. As a result, the unjacketed region of the optical fiber outside the feed through tube breaks easily because any support and strain relief provided by the boot extending between the jacketed fiber and the feed through tube is no longer available when the boot loosens.